Filtration Media

Acoustic Media

Purolator Facet, Inc. offers an extensive line of porous metal face sheet membrane materials for acoustic treatment. Rayl values from 3 to 140 CGS can be provided with or without a supporting perforated sheet. Rayl value is defined as a ratio of pressure drop to flow. It is selected based on sound intensities and pressure levels. Panel sizes range from 20" x 30" to 24" x 48". Larger custom sizes are also available. Non-linearity factors are usually less than 2.0 based on 200/20 CGS rayl readings. Thickness varies from .005" to .071".

Our current offerings include three types of acoustic face sheet material:

Poromesh®--Single layers of wire cloth diffusion bonded at points of crossover and calendered.

Poroplate®--Multi-layers of wire mesh, all diffusion bonded and calendered.

Poroplate®--Mesh and perforated plate combinations with one or more layers of wire cloth diffusion bonded and calendered to obtain given rayl value and then diffusion bonded to perforated plate.

These combinations are normally applied to single degree of freedom applications.

Purolator acoustic Poromesh® and Poroplate® diffusion bonded porous metals are used to provide acoustic flow resistance for Helmholtz resonator sound absorption applications and other noise abatement applications. The applications include face sheet and septum material for single or two-degree of freedom treatments.

The face sheet or septum porous metal membrane operates as a viscous damper of air particle velocities and is usually located about one fourth of the wave length of a peak or dominant frequency from the wall of the resonator cavity. The flow resistance required for optimum operation is determined by analysis of sound energy levels, complex acoustic impedance requirements for a sound absorbing structure and correlation of these with steady state fluid flow resistance of permeability values.

Porous material permeability is measured by gas flow testing candidate material over the required range of flow rates corresponding to face velocities of 20 to 500 centimeters per second (cm/sec). The resultant data is then reduced to show acoustic resistance in centimeter/gram/second rayls as a function of flow velocity and plotted on standard logarithmic graph paper.

Plotting rayl values as a function of low velocity on linear graph paper normally approximates a straight line, the slope of which can serve as a measure of non-linearity. Lower ratios of non-linearity are preferred since they permit acoustic treatment over a wide band of operating conditions (primarily due to temperature and resultant air density).

Rayl value is defined as the ratio of pressure drop to flow. It is selected based on sound intensities and pressure levels.

Non-linearity factor (NLF) is normally defined as a ratio of two rayl values at two different velocities, i.e., R 200/20.

Product selection for application should be based on the following:

Intended applications (duct work, face sheet, or septum)

Rayl value

Linearity

Forming over constant or changing radii

Structural strength (torsional, beam, and tensile)

Protection from galvanic corrosion by isolation

Bonding to perforated plate (metallic to metallic)

Drum face sonic load

Thermal shock

Alloy 304, 316, Nickel, Monel

Weight

Thickness

Panel size

Secondary brazing or welding

Surface texture (boundary layer control)

.

Acoustic Technical Data Q & A

What materials can be used and what are their associated lead times?

Materials are available in 304, 304L, 316, 316L with lead times of 6-8 weeks, depending on quantity. Alloys such as 321 and 347 are also available, but with extended lead times of 12-16 weeks depending on quantity.

What sheet sizes are available?

Sizes up to 48" x 48" are available depending on application. Larger welded panels are also available.

What is employed in heat treatment of acoustic media?

All Purolator diffusion media products are subjected to a controlled environment. The result is an oxidation-free product without sensitization or delamination problems. All heat treatment and final inspection is performed in accordance with rigid Purolator processes and product specifications to ensure conformance to design and contract requirements by part number and drawing.

What are our forming capabilities?

Fully annealed acoustic media is adaptable to all conventional forming and shearing operations within its metallurgical limits and without significant change to its nominal rayl value.

How are Rayl numbers verified?

We use a 1", 2" or 4" diameter flow port opening and Meriam laminar flow elements integrated with pressure transducers and digital readout. Flow data is then evaluated using a spreadsheet to generate rayls VS velocity (CGS).